In recent years, it has been obvious that the propagation characteristics of electromagnetic waves are able to be controlled by periodically disposing conductor patterns having a specific structure (hereinafter, referred to as a “metamaterial”). Particularly, a metamaterial formed so as to suppress the propagation of electromagnetic waves in a specific frequency band is called an electromagnetic band gap structure (hereinafter, referred to as an “EBG structure”), and an attempt to suppress noise propagation between a power plane and a ground plane by applying the EBG structure to an interconnect substrate has been reported.
For example, Patent Document 1 (Specification of U.S. Patent Application Publication No. 2005/0195051) discloses a so-called mushroom-type EBG structure, as shown in FIG. 24, in which a plurality of insular conductor elements are disposed on a layer between two conductor planes opposite to each other and each of the insular conductor elements is connected to a conductor plane through a via, and a modified example thereof.